!!$
!!$ ---- This include statement should always be included in any fortran 
!!$ ---- program using the fxtc libraries
!!$
interface
!!$
!!$ --- This must be the first call to the fxtc library
!!$     pdb (input): the pdb filename , its length must not exceed 140 characters
!!$     xtc (input): the xtc filename , its length must not exceed 140 characters
!!$     n (output): integer, the number of atoms of your system. The library checks
!!$     if the xtc and the pdb file are incosistent
!!$    
    subroutine F_openfiles(pdb,xtc,n)
       implicit none
       character(len=140) :: pdb,xtc
       integer :: n
    end subroutine F_openfiles
!!$
!!$ --- Read the atomic labels of the system. It is usually used only
!!$     once after the first call to F_openfiles.
!!$     labels(output:  is a len=4 character array obtained from 
!!$                     the label sequence of your pdb file
!!$

    subroutine F_readlabels(labels)
      implicit none
      character(len=4) :: labels(:)
    end subroutine F_readlabels
!!$
!!$ --- Read the co box vectors the coordinates for each step of the simulation.
!!$     They are in nanometers *not* Angstroms@!@!
!!$
!!$
!!$     co (output): real(4) array(:) of length 9. It correspond to a 3x3c matrix, 
!!$                  but with a C *not* fortran ordering. 
!!$     x, y, z (output) : real(4) array(:) whose dimension is the number of atoms
!!$     skip (input) : is a logical parameter. If .true. the actual step is skipped             
!!$                    if it is .false. or not present the step is normally read in.
!!$     F_readnext(output) : is an integer corresponding to the step number read
!!$
!!$
    integer function F_readnext(co,x,y,z,skip)
        implicit none
        real(4) :: co(:),x(:),y(:),z(:)
        logical, optional :: skip
     end function F_readnext
end interface

